There is no ultimate fix for the infamous Heavy Car Bug.

However, if you happen to experience it there are some things you can do to make the situation a lot better.
In this guide I'll show you one of those; a simple but powerful config tweak.

"OneFrameThreadLag" is a hidden setting in Rocket League that can cause a slight delay in the game's responsiveness. When enabled, it adds a small lag (about one frame) between the game's calculations and the way it displays on your screen. This can make your actions feel less responsive, especially if you're trying to make quick moves.

This setting forces the game to wait a little longer before rendering the next frame, which can help with system stability, but at the cost of input responsiveness. Disabling "OneFrameThreadLag" can make the game feel more immediate and smoother, especially if you have a high-performance PC or a stable internet connection.

[1]

Open the Rocket League config file with a text editor (like Notepad).
You can find it in the following location:

C:\Users\<YourUsername>\Documents\My Games\Rocket League\TAGame\Config\TASystemSettings.ini


[2]

Find the line that says:
OneFrameThreadLag=True

Change the setting to:
OneFrameThreadLag=False

If you are using Nvidia and have "Low Latency" enabled the effect will be smaller, but it can be still worthy.

You don't need to make the config file "Read Only". Updates should not overwrite it, but you may check it time-to-time after bigger ones!

The in-game FPS limiter does the job, but your FrameTimes can be all over the place. If you feel like your game is not smooth enough despite having a lot of FPS, you should try MSI Afterburner + Rivatuner Statistics Server to control your FPS and FrameTime numbers. It's pretty easy to setup and can be extremely useful. Look for a guide on youtube about how to install those!